1. Field of the Invention
This invention relates to a focus detecting device which detects the focusing condition of an objective lens by projecting a light flux from a light source onto an object through the objective lens and by sensing the light flux after it is reflected from the object and more particularly to a focus detecting device adapted for an optical apparatus, such as a camera, a video camera or the like.
2. Description of the Prior Art
Focus detecting devices of the kind detecting the focusing condition of an objective lens by projecting a light flux from a light source onto an object through the objective lens and by sensing with a sensor the light flux after it is reflected from the object have been known and proposed, for example, in Japanese Laid-Open Patent No. SHO 57-73709 (laid open date: May 8, 1982).
The device disclosed in the above cited patent application is capable of detecting the focusing condition in a fairly satisfactory manner, even for a dark or low-contrast object. The device has the advantage of the so-called active type focus detecting device which permits a relatively simple arrangement of the sensor and the signal processing circuit. In addition, the device is not degraded by reflection from the lens surface of a photo-taking lens.
However, when used for a camera which has an interchangeable lens, such as a single-lens reflex camera, this device of the prior art presents the following problem: If eccentricity or mis-alignment occurs between a camera body and a photo-taking lens in mounting the latter on the former due to an assembly error either on the side of the camera body or on the side of the lens, focus detecting accuracy is greatly decreased.
An object of the present invention is therefore to provide a focus detecting device in which the detecting accuracy is never degraded even when the device is applied to a camera of the kind using an interchangeable lens.
Another object of the invention is to provide an active type focus detecting device which is capable of performing focus detection with great accuracy.
These and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.